The present invention relates to a bridge igniter, such as, for example, a reactive bridge igniter.
Although applicable to any bridge igniter, the present invention and the set of problems on which it is based are explained in relation to a bridge igniter for triggering airbags and seat-belt tighteners in motor vehicles.
Bridge igniters may be made up of a resistance layer and a reactive layer disposed on top of it, the resistance layer being heated using an electric current. The reactive layer, also heated, may react exothermically and initiate a pyrotechnic material lying on top of it.
The electrical resistance of the bridge igniter or of the resistance layer may not be adjusted independently of the material of the reactive layer or its thickness, because these two layers are in electrical contact with each other. Thus, a greater energy input may be required to generate the Joule-effect heat required to fire the reactive bridge igniter.
Moreover, under certain circumstances, several adhesive layers may be required between the resistance layer and the reactive layer for an improved mechanical adhesion, which may also increase the process costs.
A metal ignition bridge that is separated from a pyrotechnic ignition charge by an insulating layer is discussed in European Published Application Patent No. 05 10 551. The pyrotechnic ignition charge is started by heating the metal ignition bridge. An adhesive layer for the hybrid bonding of two substrates is discussed from German Published Patent Application No. 27 01 373. Swiss Published Patent Application No. 649 150 discusses an insulating layer that separates the pyrotechnic ignition charge from the metal ignition bridge. In this manner, the complete ignition resistance may also be joined to the substrate. An ignition element for pyrotechnic payloads and a corresponding method are discussed in German Published Patent Application No. 197 32 380. This may specify that electrical contact surfaces are connected to the resistance layer to supply electricity to it. It may also be indicated therein that the resistance layer is configured in the shape of a bridge. A pyrotechnic ignition system having an integrated ignition circuit is discussed in German Patent Publication 199 40 201. This may specify that the bridge igniter is disposed on a substrate. This substrate may also be an integrated circuit that supplies electrical energy to the resistance layer.
An object of the present invention may include providing bridge igniters which may minimize the energy input required to fire the pyrotechnic material and at the same time may allow the ignition bridge resistance to be adjusted over a greater range, independent of the thickness of the reactive layer.
According to an exemplary embodiment of the present invention, the bridge igniter may have: a resistance layer which has a given electrical resistance and which may be heated by an electrical current, an electrically insulating layer that is disposed on the resistance layer and has a given thermal conductivity, a reactive layer that is disposed on the insulating layer, the insulating layer transmitting the heat that is produced in the resistance layer to the reactive layer, thereby causing the latter to undergo an exothermic reaction, and a pyrotechnic layer that is disposed on or above the reactive layer and may be set off by the exothermic reaction of the reactive layer.
According to an exemplary bridge igniter of the present invention, the resistance of the bridge may be adjustable over a greater range and may be independent of the reactive layer material and its thickness. Thus, the electrical resistance of the resistance layer may be the sole factor determining the energy input required to fire the bridge igniter. The electrical separation of resistance layer and reactive layer by the insulating layer may allow the electrical resistance of the resistance layer to be adjusted independently of the material characteristics and thickness of the reactive layer.
Moreover, the insulating layer may simultaneously function as an adhesive layer between the resistance layer and the reactive layer. Additional production steps for forming such an adhesive layer may be eliminated.
Moreover, the insulating layer may be used as a diffusion barrier between the resistance layer and the reactive layer, a diffusion of atoms and/or ions of the reactive layer material into the resistance material, for example, thereby being prevented.
According to an exemplary embodiment, the insulating layer may be formed as an oxide layer, such as, for example, as a copper oxide or silicon dioxide layer. These layers, which may have a given thickness, may simultaneously ensure a good electrical insulation and a thermal connection between the resistance layer and the reactive layer.
According to another exemplary embodiment, the insulating layer may have a thickness of approximately 50 to 100 nm. Such thicknesses may be required to be adapted to the corresponding materials in such a manner that they fulfill the given characteristics.
According to another exemplary embodiment, the resistance layer may be made of palladium or nickel-chromium.
According to another exemplary embodiment, the reactive layer may be made of zirconium or hafnium.
According to another exemplary embodiment, the resistance layer has an adhesive layer, for example, a titanium layer, disposed on it. This adhesive layer may provide a better mechanical adhesion of the reactive layer or the insulating layer on the resistance layer. For example, the insulating layer itself may function as an adhesive layer between the resistance layer and the reactive layer. Consequently, the step of manufacturing an additional adhesive layer may be omitted.
According to another exemplary embodiment, a co-reactant may cooperate with the reactive layer to produce an exothermic reaction in it. As a result, an additional amount of heat may be released which may be required to set off the pyrotechnic material.
According to another exemplary embodiment, the insulating layer may function as a co-reactant. The reactive layer may reacts exothermically when it cooperates with an oxide layer, for example. Thus, no additional co-reactants may have to be produced.
According to another exemplary embodiment, the reactive layer may have a co-reactant, such as, for example, an oxide layer, disposed on it. This co-reactant may also be used to initiate an exothermic reaction in the reactive layer.
Another exemplary embodiment may provide a plurality of reactive layers and co-reactants in alternating sequence to produce a multi-layer structure, the co-reactants being formed in particular as oxide layers of the material of the corresponding reactive layers. This may result in a sandwich-type structure, which may contribute to improving the course of the reaction by enlarging the reaction surface.
According to another exemplary embodiment, the insulating layer may function as a diffusion barrier between the resistance layer and the reactive layer.
According to another exemplary embodiment, electrical contact surfaces, for example, gold plates, may be connected to the resistance layer in order to supply electricity to it. The size, shape and material of the contact surfaces may be adapted to a desired electrical energy to be supplied.
According to another exemplary embodiment, the bridge igniter may be disposed on a substrate, for example, a silicon substrate, a ceramic, a plastic or an integrated circuit (IC). When the bridge igniter is disposed on an integrated circuit, the contact surfaces may not be required, because the resistance layer may be supplied with electrical energy via supply leads of the integrated circuit. Thus, the overall structure may be simplified and a more compact component may be produced.
According to another exemplary embodiment, the resistance layer may be configured in the shape of a bridge. As a result, the resistance of the resistance layer may be increased and more Joule-effect heat may be generated.